The owners of the big owe are trying to get an NFL game for next year (or at least they were earlier this year) so I don't see why a CFL game isn't possible.
"We're always open for opportunities to host sporting events," Alain Larochelle, vice-president of business development for Olympic Stadium operator Olympic Park, said in a statement. "The Montreal Olympic Stadium has a rich history with North American football, especially with the CFL, the Grey Cup and the Montreal Alouettes, who still hold the record for the largest sport attendance in the history of the stadium.
"We would be very interested in hosting an NFL game and we are eager to show the numerous planned investments and the many possibilities of the Montreal Olympic Stadium to the promoters around the globe."
https://www.tsn.ca/montreal-s-olympic-stadium-expresses-interest-in-hosting-nfl-games-1.1616317